Drive systems have remained primarily centered around the same simple concepts for many years, typically relying on some sort of rotary power output, such as a car engine or electric motor, wherein the rotary drive power, in turn, is converted into linear motion of the entire system. These existing drive systems can be easily separated amongst the following different and distinct types of motion.
A first type of drive system is a tank drive. This type of drive train maneuvers by changing the speed of either side of the system, allowing a robot to drive forward and backward and also to turn. By speeding up or slowing down rotation on one side relative to the other, the robot is able to turn; and a small difference in the displacement of opposite sides is magnified causing the difference in displacement (or speed) to rotate the entire robot. A downside of this approach is that, at high speeds, a minor difference in rotation can lead to large directional changes, and this often is impractical at high speeds.
A second type of drive system uses Ackerman steering/articulation. These drive trains work by mechanically altering the orientation of one set of wheels, usually forward wheels, so that the direction of motion is turned along that new orientation. Typically, in these systems, only either the rear wheels or the front wheels are powered, much like in a car. Although more controllable at high speeds, robots employing Ackerman steering/articulation are much less maneuverable, and tend to have delayed or choppy turning—depending on how the steering is implemented.
A third type of drive system uses omni-wheels (i.e., omni-directional wheels) and Mecanum drive. Robots that employ this system typically use tank drive associated with unique sets of wheels. These wheels are either omni or Mecanum wheels—the common characteristic being that they have rollers mounted in the wheel set either perpendicular to the direction of overall rotation (omni) or at a 45 degree angle to it (Mecanum). These wheels work by generating a vector quantity. When normally driving, the robot behaves as any other tank-drive robot, but when driving the wheels against each other, a vector is generated which causes atypical movement. For example, when running Mecanum wheels towards each other the North-South force cancels causing the robot to move directly east or west, as if sliding. Omni wheels function in a similar way, but with perpendicular rollers. A disadvantage to these approaches is that the vector force drastically reduces power; and, due to the rollers, robots employing these systems can slide easily when outside forces act on them or when they attempt to change direction.
A fourth type of system is swerve drive, which tends to be the most difficult drive train to implement. Swerve drive works by independently rotating the entire orientation of each wheel. Additionally, each wheel is independently powered, meaning that the entire motor assembly, gearing, wheel and mounting are all rotated carefully and precisely so that neither mechanical nor electrical components are damaged. The end effect is that the robot is able to move in any direction, but that there is a delay in change of direction; moreover, a large number of safety procedures typically are needed to prevent the robot from damaging itself. Physically, these requirements and characteristics typically make swerve robots heavy, slow, and difficult to build.